Spectrometers are used in chemical analysis for identification of compounds in a sample. In some cases a quick indication of presence of particular compounds in a sample is needed, while at other times the goal is complete identification of all compounds in a chemical mixture. Accordingly, samples may be taken directly from the environment and analyzed or may be prepared by processing and/or separating the constituents before spectrometric analysis.
Spectrometers based on ion mobility have been used to detect various chemical and biological compounds. Such spectrometers include ion-mobility spectrometry (IMS) and differential ion mobility spectrometers (DMS) which are also known as field asymmetric waveform ion mobility spectrometers (FAIMS)
Commercially available IMS systems are based on time-of-flight (TOF-IMS), i.e., they measure the time it takes ions to travel from a shutter-gate to a detector through an inert atmosphere (1 to 760 Torr.). The drift time is dependent on the mobility of ions in a low electric field based on size, mass and charge, and is characteristic of the ion species detected. TOF-IMS has been used for detection of many compounds including narcotics, explosives, and chemical warfare agents, and at least one TOF-IMS system has been adapted for use in a field-portable device for detection of bacterial spores in the environment.
DMS devices offer an alternative to the low field TOF-IMS ion mobility process. In DMS, ion filtering is achieved based on accentuating differences in mobility of ionized molecules in a high field. The high field mobility differences are used for “signature” identification of chemical species in an ionized sample. DMS filtering is an efficient process, combining controlled neutralization of unselected ion species while passing selected ion species for detection.
There is a strong and continuing interest in improved approaches to sample characterization, particularly as may be provided in compact and portable devices.